Writing instrument



FIG. 1 is a rear view of a writing instrument of my new design;

FIG. 2 is a right side view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a bottom plan view thereof; and,

FIG. 6 is a top plan view thereof.

The broken lines showing the top are included for the purposes of illustrating environment and form no part of the claimed design. 

The ornamental design for a writing instrument, as shown and described. 